The smallest 34 cm fin being recommended for this board should be fine with your 5.7 m2 sail and your light weight whereas a 38-40 cm fin should be fine with your 7.0 m2 sails. The 48 cm fin is good for sails in the 8.x to 9.x m2 range, however.

Take a freeride fin, this should be a nice match for the board character. I would choose a 34 cm for both your 5.7 and 6.2 m2 sail since you're a light weight. A size of 38 cm should be fine with a 7 m2 sail.

Since you seems to be in France, I suggest you have a look at Select Edge Freeslam fins :

You can order a 35 cm and a 39 cm fin, both in standard Tuttle box *. Together with the stock 48 cm fin that you already own, you'll be covered from 5.7 m2 up to 9.x m2.

When the fin is way too large for the small sail you have in high wind and your light weight, you'll have lots of trouble to control the big board, keep the nose down and not to tailwalk. Allways match the size of the fin with the size of your sail.

Cheers !

JM

(*) : you can put a standard Tuttle box fin into a deep Tuttle finbox of your Compact but you will need 2 cm longer screws. My suggestion to order both fins in standard Tuttle finbox and not deep Tuttle finbox is that you can use these fins in any other board that come with a standard Tuttle finbox.